Metal eating bacteria

I was reading the headlines on CNN this morning, and this one grabbed my eye. The gist of the article is that researchers from Dalhousie University, in Halifax, Nova Scotia, examined some sediment brought up from the wreck of the Titanic.  Scientists have been visiting the wreck site in the North Atlantic for about 25 years, since it was initially discovered by Robert Ballard in 1985. Surveys of the wreck were initially accomplished by remote observation, but within a year or two, manned submersible were visiting the site and retrieving artifacts. The condition of the wreck significantly increased our understanding of how the tragedy occurred, however the common consensus among scientists was that access to the site should be restricted to maintain it in as pristine of condition as possible.

Ballard’s initial survey of the wreckage indicated that significant corrosion of the steel superstructure has occurred over the past 100 years. The exposed structure is covered with growths termed “rusticles,” which are large, icicle-like formations of rust. These structures turned out to be teeming with biofilms of bacteria, which were recovered and brought back to the surface. When examined in the laboratory, it was found that these organisms very readily grew on and began to break down any metal structures that there were introduced to. The researchers at Dalhousie University have conjectured that the wreck of the Titanic will degrade into a rust-colored patch on the ocean floor within the next 30 years, and little physical evidence of the tragedy will remain after that point.

So here’s a bonus opportunity: based on what we know about microbial growth (hint: Chapter 6,) what can we surmise about what the scientists at Dalhousie had to consider when trying to growth these bacteria in the lab? There are several things, so please comment here!

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on December 12, 2010, in Bonus!, Microbes in the News. Bookmark the permalink. 9 Comments.

  1. Maybe … [the] … effect of oxygen?

    edited by DS, to promote as many comments as possible

  2. (Prof. Singleton has a beef to pick with my article!)
    [W]hat’s with the “good bacteria”/”bad bacteria” stuff, other than making for good press? Despite the old Lysol (R) commercials, there is no such thing as a “bad germ”; bacteria are bacteria! The sulfate reducing bacteria are a good example. While they are a pain in the pocketbook for the oil industry, they are immensely important in many environmental systems. Take a hike through an estuarine environment someday and enjoy the “eau de H2S” bubbling up around your shoes.

    That’s my $0.02 worth.

  3. Sangwon Ha: So what oxygen levels did you have in mind at the bottom of the ocean that would be an issue for laboratory cultures? Also, rust formation requires oxygen; where does the oxygen come from?

  4. 1) The oxygen saturation level related to the hydraulic pressure can be the possible oxygen levels to be considered because laboratory is usually under normal atmospheric pressure.
    2) The oxygen came from the water. Oxygen is resolved in the water and normally fishes are using that. The rust formation, by using the oxygen from water, is following these chemical equations.
    2Fe(s) + 2H2O(l) + O2(g) ==> 2Fe2+(aq) + 4OH(aq)
    Fe2+(aq) + 2OH-(aq) ==> Fe(OH)2(s)
    Fe(OH)2(s) =O2=> Fe(OH)3(s)
    Fe(OH)3(s) ===> Fe2O3.nH2O (AKA rust)

    One point of the article is that this is not exclusively a chemical reaction, although these balanced equations do demonstrate where the rust comes from in the absence of biological activity. The Titanic is being affected by the microorganisms, which are accelerating the rusting process. The deep ocean is actually has relatively abundant levels of oxygen, which promotes the change from Fe0 to Fe2+ due to chemical reactions as above. Bacteria potentially then alter the balance by rapidly removing the Fe2+ biologically, shifting the equilibrium further. —DS

  5. Ah, a great question: “where does the oxygen come from?”. The “editor” cut the answer from my previous post, most probably because I would have hogged all the bonus points. But, I will forge ahead any way. To do so requires a review of some basic biochemistry and microbial physiology.

    From a metabolic, or biochemical, perspective the general term respiration is a process used to regenerate “reducing potential” (in the form of compounds such as NADH, etc.) formed when various reduced compounds (e.g. glucose) are oxidized to carbon dioxide and water. In aerobic respiration NADH is oxidized back to NAD by oxygen in a series of reactions taking place across a membrane. The protons (H+) generated in these reactions are transported outside of the membrane creating a charge separation (+ outside, – inside). The energy of this charge separation can be used to generate a variety of cellular activities, one of the most important is generating ATP. That “energy gradient,” however, can be used to carry out other cell functions such of transport processes or flagella rotation for bacteria.

    Bacteria, which began their evolutionary history long before O2( was around, developed a variety of ways to deal with the metabolic problem of regenerating NAD (and similar co-factors). Like their eukaryotic cousins, bacterial cells oxidize an amazing variety of reduced compounds (some carbon, some non-carbon) to generate energy for growth. One way is via fermentation where a product from part of the pathway is reduced to regenerate NAD.
    For example:
    Glucose + NAD –> Pyruvate + ATP + NADH
    Pyruvate + NADH –> NAD + Ethanol + CO2 +H2O

    Fermentation, as you may recall, yields only 2 or so ATPs/glucose, however a second process, anaerobic respiration has much higher ATP yields. In a manner analogous with aerobic respiration, various types of bacteria use compounds such as sulfate, nitrate, etc. as ways to regenerate “reducing potential.” For example, the sulfate-reducing bacteria (SRB) oxidize a variety of carbon compounds (glucose is one) to acetate + CO2 + H2O. The oxidation is coupled (remember, for every oxidation there must be an equal reduction) with reducing sulfate to H2S, which at neutral pH exists as a mixture of HS- and S-2, both of which are very corrosive (similar to rust formation).

    Anaerobic respiration also “pumps” protons across the cell membrane. Again, that energy gradient can be used to generate ATP or carry out other cellular processes.

    Now that you have (hopefully) waded through all of the above, the answer to “the great question: ‘where does the oxygen come from?’ ” should be obvious. Oxygen, as O2, is not needed for “metal eating,” or better corrosion processes.

  6. No worries about hogging all of the bonus points; if I run out, I’ll just print up some more!

    I think Sangwon above is correct about the origin of the oxygen for the rusting process; it is from dissolved O2 in seawater, however the microbes growing on the shipwreck are speeding up the process by utilizing the iron ions generated by chemical rusting.

    My initial thought was that it was due to anaerobic respiration of Fe metal, but I can find no biological reaction using non-ionic iron in metabolism.

    Back to the original bonus opportunity; anything other than oxygen levels that potentially present an issue to growing these microorganisms in the laboratory?

  7. Salinity would also be a factor – the microbe would need to be a halophile. Also how it gets it energy, obviously not from the sun, therefore it must be a chemotroph. Where does it get its carbon? At that depth, I’m not sure.

    • You’re definitely right about the carbon; two miles down in the ocean is pretty limited for reduced carbon compounds like sugars. These organisms are likely chemolithotrophs, getting their source of energy from the chemistry of iron, and their carbon from inorganic carbon dissolved in the sea water.

  8. Getting “their carbon from inorganic carbon”; the old “Wood-Werkman” reaction still works!

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